1. Filed of the Invention
The present invention relates to a stator of the AC generator adapted for use in a vehicle and a method of manufacturing the same and, in particular, to a stator of the AC generator adapted for use in a vehicle and a method of manufacturing the same which serve to enhance rigidity by increasing the space factor of a stator coil which is housed within the slot portion.
2. Description of the Related Art
FIG. 13 is a cross-sectional view illustrating the arrangement of a conventional AC generator adapted for use in a vehicle.
In the conventional AC generator adapted for use in a vehicle, a Lundell type rotor 7 is rotatably fitted into a case 3 comprising a front bracket 1 and a rear bracket 2 each made of aluminum by way of a shaft 6, while a stator 8 is fixedly fitted to the surface of the inner wall of the case 3 in such a way that the stator 8 covers the outer periphery of the rotor 7.
A shaft 6 is rotatably supported against the front bracket 1 and the rear bracket 2. A pulley 4 is fixedly fitted to one end of this shaft 6 so that the rotational torque of the engine may be transmitted to the shaft 6 by way of a belt (not shown).
A slip ring 9 which supplies a current to the rotor 7 is rigidly fitted to the other end portion of the shaft 6, and a pair of brushes 10 is housed within a brush holder 11 disposed within the case 3 so that it may lie in slideable contact with the slip ring 9. A regulator 18, which regulates the output voltage of the stator 8, is adhered to a heat sink 17 fitted on the brush holder 11. A rectifier 12 is electrically connected to the stator 8 to rectify the alternating current generated in the coil of the stator 8 into the direct current and is mounted within the case 3.
The rotor 7 comprises a rotor coil 13 which generates the magnetic flux when a current flows therein, and a pair of pole cores 20, 21 provided to cover the rotor coil 13 and be magnetic poles as a result of the magnetic flux generated by the rotor coil 13. The pair of pole cores 20, 21 are made of iron, and a plurality of claw-shaped magnetic poles 22, 23 are provided on the outer circumference of the poles cores 20, 21 so as to protrude at equiangular intervals in their circumferential direction. The pole cores 20, 21 are fixedly fitted to the shaft 6 in an opposed relation to each other so that their claw-shaped magnetic poles 22, 23 are able to engage with each other. Further, fans 5 are fixedly attached to both axial ends of the rotor 7.
The stator 8 comprises a stator core 15 and a stator coil 16 achieved by winding a conductor wire around the stator core 15, and an alternating current is generated by alternating the magnetic flux of the rotor 7 with the rotation of the rotor 7.
In such conventional AC generator, the current is supplied to the rotor coil 13 from a battery (not shown) by way of the brush 10 and the slip ring 9, thereby generating the magnetic flux. Owing to this magnetic flux, the claw-shaped magnetic poles 22 of one pole core 20 are magnetized to N polarities, while the claw-shaped magnetic poles 23 of the other pole core 21 are magnetized to S polarities. On the other hand, the rotational torque of the engine may be transmitted to the shaft 6 by way of the belt and the pulley 4, causing the rotor 7 to rotate. As a result, a rotational magnetic field is imparted to the stator coil 16, and an electromotive force may take place in the stator coil 16. This AC electromotive force passes through the rectifier 12 to be rectified into a direct current, its voltage is regulated by the regulator 18 and the battery is electrically charged.
Here, in a common AC generator for use in a vehicle, the stator core 15 has a core back portion 15a, substantially rectangular tooth portions 15b protruding from the core back portion 15a in the direction of the inner circumference thereof, and notch portions 15d provided on the outer circumference of the core back portion 15a so as to oppose to the tooth portions 15b respectively. The tooth portions 15b are provided, for example, 36 at the equiangular intervals as viewed in the circumferential direction, and a slot portion 15c which is interleaved between adjacent tooth portions 15b, 15b may serve as a space into which the coil is inserted. The 36 tooth portions 15b are each opposed to 12 nailed-shaped magnetic poles 22, 23 by way of a minor clearance as viewed in the inner direction, and the magnetic flux caused by the rotational magnetic field flows as indicated by broken line of FIG. 14. Incidentally, in FIG. 14, for the sake of convenience, the claw-shaped magnetic poles 23 are not shown.
Accordingly, the major portion of each tooth portion 15b, which serves as a passageway for a predetermined magnetic flux to pass through has preferably a uniform cross-sectional area because the magnetic flux is not branched off and is not increased or decreased, and does not increase or decrease there. That is, in order to unify the density of the magnetic flux within the tooth portion 15b, the shape of each tooth portion 15b is preferably of rectangular form rather than of trapezoidal form. Further, the tip portion of each tooth portion 15b has a circumferentially extending portion so as to exclude leakage of the magnetic flux to smooth the density of the magnetic flux at the air gap.
Next, a conventional method of manufacturing the stator 8 is described with reference to FIGS. 15 and 16.
First, a thin steel plate member is supplied to a press processing machine (not shown) to form two-way belt-shaped members 30 each having the core back portion 30a and the tooth portion 30b from the one-way thin steel plate member, as shown in FIG. 15. At this time, arcuate notch portions 30c are provided on the outer circumference of the core back portion 30a so as to oppose to the tooth portions 30b respectively. With the core back portions, tooth portions and the notch portions aligned with each other, the two-way belt-shaped members 30 are overlapped and are wound in a hollow cylindrical form. Next, the cylindrically wound belt-shaped members 30 are welded for integration, and then are subjected to insulating coating to obtain a hollow cylindrical stator core 15, as shown in FIG. 16. In this stator core 15, the core back portion 30a, tooth portion 30b and notch potion 30c of the belt-shaped member 30 are each consecutive in the axial direction to form a core back portion 15a, a tooth portion 15b and a notch portion 15d.
Next, the tip portion of a group of coils formed in the form of a star (not shown) is deformed to insert into each slot portion 15c of the stator core 15 from the side of the inner circumference thereof, while the part of the coils extending from the slot portion 15c is deformed in the circumferential direction to obtain the stator 8.
Incidentally, this conventional method of manufacturing the stator is described in, for example, Japanese Unexamined Patent Publication No. 60-7898 and Japanese Patent No. 2541381.
Here, in the belt-shaped member 30 obtained by punching the thin steel plate, as shown in FIG. 15, the major portion of each tooth portion and each slot portion is of rectangular form. When the belt-shaped member 30 is wound in the from of a hollow cylinder, the tip end portions of the tooth portions each become close to each other in the circumferential direction with the result that each slot portion achieves a substantially trapezoidal form which spreads in the outer circumferential direction, as shown in FIG. 16.
Further, used for the stator coil 16 is a conductor wire of circular form in cross section in view of the workability and ease of availability.
In the AC generator, in order to generate the amount of magnetic flux for electrical generation as many as possible, it is necessary to accommodate a large number of conductor wires, that is, a conductor wire having as many the number of turns as possible within each slot portion 15c. In the conventional stator 8, as shown in FIG. 17, since a conductor wire of circular form in cross section is used for the stator coil 16 to accommodate within the slot portion 15c of substantially trapezoidal form, the overall cross-sectional area of the conductor wire which may be accommodated within the slot portion 15c cannot exceed (.pi./4).times.D.sup.2.times.n theoretically. Incidentally, D denotes the diameter of the conductor wire, and n denotes the number of conductor wires which may be accommodated within the slot portion. In view of the presence of thickness of the insulating coating of the stator core 15 and the stator coil 16, the ratio occupied by the overall cross-sectional area of the conductor wire relative to the slot area (space factor) will account for approximately 50 to 66%.
In this kind of AC generator, in order to improve the output, it has been necessary to accommodate a large number of conductor wires, that is, a conductor wire having as many turned as possible within the slot to generate a large amount of magnetic flux caused by the rotational magnetic field.
In order to achieve a conductor wire having as many turns as possible within the same inner area of the slot, one may make the diameter of the conductor wire thin. However, if the diameter of the conductor wire is made thin, then the resistance of the conductor wire is increased, which makes it impossible to obtain a sufficient output while, at the same time, increasing heat generation in excess of the permissible temperature of the conductor wire. Therefore, how many times a thick conductor wire can be turned serves as a key to achieving a high output. This amounts to increasing the space factor, the ratio occupied by the cross-sectional area of the wire relative to the internal area of the slot, but if it is increased, then the friction of the turns of the wire especially within the slot of the stator core while being turned causes the insulating coating film of the wire to be broken, or results in the loss of the withstand voltage performance between the rotor core and the stator coil.
In order to eliminate such drawbacks, a technique of aligning a coil of rectangular cross-section into the slot of the stator core for accommodation is described in, for example, Japanese Examined Patent Publication No. 8-13182. However, in this conventional embodiment, since the cross-section of the slot is formed into a substantially rectangular form in order to accommodate the coil of rectangular cross-section without any waste of space, the major portion of the tooth portion is formed into a trapezoidal form spreading in the direction of outer circumference resulting in a stator having a magnetically wasteful portion. Therefore, in order to achieve an equivalent amount of magnetic flux as that of the tooth portion whose major portion is formed into a rectangular form, it has been necessary to make the slot area smaller correspondingly. Conversely, if the slot areas are made as equal, then the amount of magnetic flux is decreased and a sufficient output cannot be achieved.
Further, due to the recent trend for achieving high output, the electromagnetic noise caused by vibrations of parts generating during electrical generation has caused a problem. The major cause of the electromagnet noise is mainly due to the radial vibrations of the stator core 15 (stator), as shown in FIGS. 18 to 20. In order to suppress those, a noise suppressing member has been fitted into the outer circumference of the stator core, or the thickness of the core back portion of the stator core is increased so as to increase rigidity of the stator, which, however, have not served as a realistic countermeasure because they accompany increase of weight or cost.